Radiation treatment planning and delivery using collision free regions

ABSTRACT

Collision free regions are predetermined for one or more class solutions. Each class solution has defined limits for allowed field geometry variations. Collision free regions in planning can be defined as a set of allowed isocenter positions relative to a fixation device. The collision free regions may be visualized by a user to plan for field geometry and isocenter position tradeoffs. Collision free regions in delivery can be defined as a set of allowed couch support coordinates. The treatment fields in a radiation treatment plan can be checked against the collision free regions in delivery to determine whether they will pose any collision risks.

BACKGROUND

Modern radiation therapy techniques include the use of IntensityModulated Radiotherapy (“IMRT”), typically by means of an externalradiation treatment system, such as a linear accelerator, equipped witha multileaf collimator (“MLC”). Use of multileaf collimators in general,and an IMRT field in particular, allows the radiologist to treat apatient from a given direction of incidence to the target while varyingthe shape and dose of the radiation beam, thereby providing greatlyenhanced ability to deliver radiation to a target within a treatmentvolume while avoiding excess irradiation of nearby healthy tissue.However, the greater freedom that IMRT and other complex radiotherapytechniques, such as volumetric modulated arc therapy (VMAT), where thesystem gantry moves while radiation is delivered, and three-dimensionalconformal radiotherapy (“3D conformal” or “3DCRT”), afford toradiologists has made the task of developing treatment plans moredifficult. As used herein, the term radiotherapy should be broadlyconstrued and is intended to include various techniques used toirradiate a patient, including use of photons (such as high energyx-rays and gamma rays) and particles (such as electron and protonbeams). While modern linear accelerators use MLCs, other methods ofproviding conformal radiation to a target volume are known and arewithin the scope of the present invention.

Several techniques have been developed to create radiation treatmentplans for IMRT or conformal radiation therapy. Generally, thesetechniques are directed to solving the “inverse” problem of determiningthe optimal combination of angles, radiation doses and MLC leafmovements to deliver the desired total radiation dose to the target, orpossibly multiple targets, while minimizing irradiation of healthytissue. This inverse problem is even more complex for developing arctherapy plans where the gantry is in motion while irradiating the targetvolume. Heretofore, radiation oncologists or other medicalprofessionals, such as medical physicists and dosimetrists, have usedalgorithms to develop and optimize a radiation treatment plan.

When executing a radiation treatment plan using an external-beamradiation treatment system, it is possible that certain field geometriesmay cause machine-to-machine or machine-to-patient collisions. In suchcases, automated execution of the treatment plan may need to beprevented or else accidents may occur. Therefore, it may be desirable toevaluate collision possibilities when planning and delivering aradiation treatment to ensure the safety and usability of a radiationtreatment plan.

SUMMARY

According to some embodiments of the present invention, systems,methods, and apparatuses are provided for managing collision risks inplanning and delivery of radiation treatment plans. Collision freeregions may be predetermined for one or more class solutions. Each classsolution has defined limits for allowed field geometry variations, suchas allowed gantry angle ranges and allowed couch parameter ranges.

According to some embodiments, the collision free regions in planningcan be defined as a set of allowed isocenter positions relative to afixation device. The collision free regions may be visualized by a userto plan for field geometry and isocenter position tradeoffs. Thecollision free regions in delivery can be defined as a set of allowedcouch support coordinates. The treatment fields in a radiation treatmentplan can be checked against the collision free regions in delivery todetermine whether they will pose any collision risks.

According to some embodiments, the model used in planning and the modelused in delivery may be independent form each other. The model used inplanning and the model used in delivery may be designed to worktogether, so that each model in planning has a corresponding model indelivery. If a plan is valid according to the model in planning, it islikely to be also valid with a corresponding model in delivery.

Other embodiments are directed to systems and computer readable mediaassociated with methods described herein.

A better understanding of the nature and advantages of embodiments ofthe present invention may be gained with reference to the followingdetailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a radiation treatment system.

FIG. 2 is a schematic side view of a radiation treatment system.

FIG. 3 shows schematically a photon collimation system in a radiationtreatment system.

FIG. 4 shows an exemplary multileaf collimator (MLC) plane.

FIG. 5 shows a block diagram of an external-beam radiation treatmentsystem of FIGS. 1 and 2.

FIG. 6 shows an exemplary user interface that displays some exemplarycollision free regions for planning a radiation treatment according toan embodiment of the present invention.

FIG. 7 shows some exemplary collision free regions, as well as an imageof a patient, as viewed from the patient's feet, according to anembodiment of the present invention.

FIG. 8 shows some exemplary treatment fields according to an embodimentof the present invention.

FIG. 9A shows an exemplary user interface where some collision freeregions are superimposed on a three-dimensional image of a patient asviewed from the patient's feet.

FIG. 9B shows a perspective view of the collision free regionssuperimposed on the three-dimensional image of the patient as shown inFIG. 9A.

FIG. 10 shows a model fixation device to which collision free regionsmay be referenced.

FIG. 11A shows an image of a patient as viewed from the right side ofthe patient. A couch support device is included in the imaging. A modelfixation device is superimposed on the patient's image.

FIG. 11B shows the patient's image superimposed on the model fixationdevice as viewed from the front of the patient.

FIG. 12 shows a table including dimension values for a statisticalpatient model according to an embodiment of the present invention.

FIG. 13A shows an exemplary user interface where a user may be allowedto select one or more treatment fields from a set of predeterminedtreatment fields according to an embodiment of the present invention.

FIG. 13B shows a user interface where some exemplary collision freeregions and a model fixation device, as well as an image of a patient,are shown according to an embodiment of the present invention.

FIG. 14 shows a simplified flowchart illustrating a method ofdetermining a radiation treatment plan for delivering radiation to apatient using an external-beam radiation treatment system according toan embodiment of the present invention.

FIG. 15 shows a simplified flowchart illustrating a method ofdetermining a radiation treatment plan for delivering radiation to apatient using an external-beam radiation treatment system according toanother embodiment of the present invention.

FIG. 16 shows an exemplary user interface for using collision freeregions during delivery according to an embodiment of the presentinvention.

FIG. 17 shows a simplified flowchart illustrating a method of deliveringradiation to a patient using an external-beam radiation treatment systemaccording to an embodiment of the present invention.

FIG. 18 shows a block diagram of an example computer system usable withsystem and methods according to embodiments of the present invention.

TERMS

“Radiation” refers to any particles (e.g., photons, electrons, protonsetc.) used to treat tissue, e.g., tumors. Examples of radiation includehigh energy x-rays, gamma rays, electron beams, and proton beams. Thedifferent particles can correspond to different types of radiationtreatments. The “treatment volume” refers to the entire volume that willbe subjected to radiation, and is sometimes referred to as the“irradiated volume.” The “target structure”, “target volume”, and“planning target volume” (“PTV”) refer to tissue intended to receive atherapeutic prescribed dose.

A “radiation treatment plan” can include a dose distribution, machineparameters for achieving the dose distribution for a given patient, andinformation about the given patient. A dose distribution providesinformation about the variation in the radiation dose with spatialpositions within a treatment area of the patient. A “dose distribution”can take many forms, e.g., a dose volume histogram (DVH) or a dosematrix. A DVH can summarize three-dimensional (3D) dose distributions ina graphical 2D format, e.g., where the horizontal axis is the dose(e.g., in units of grays—Gy) absorbed by the target structure (e.g., atumor) and the vertical axis is the volume percentage. In a differentialDVH, the height of a bar at a particular dose indicates the volume ofthe target structure receiving the particular dose. In a cumulative DVH,the height of a bar at a particular dose represents the volume of thestructure receiving greater than or equal to that dose. The cumulativeDVH is generally a curve (e.g., when small bin sizes are used), whereasthe differential DVH is generally a disjoint bar graph. A drawback of aDVH is that it offers no spatial information; i.e., a DVH does not showwhere within a structure a dose is received. A dose matrix can providethe dose that each part of the body receives.

“Field geometry” describes the relation between radiation fields,patient, and support devices. Field geometries can be grouped into“class solutions.” Each class solution contains limits for allowed fieldgeometry variations, such as allowed gantry angle ranges and allowedcouch parameter ranges.

DETAILED DESCRIPTION

The present disclosure relates generally to planning and delivery ofradiation treatment using external-beam radiation treatment systems, andis more particularly directed to tools for managing collision risksduring planning and delivery of a radiation treatment. Collision freeregions may be predetermined for one or more class solutions. A classsolution may include the following information: (1) field geometrylimits, such as allowed gantry angle ranges and allowed couch parameterranges; and (2) a corresponding collision free region. Differentcombinations of field geometries, delivery machine models, and patientmodels produce the collision free regions. For radiation treatmentplanning, the collision free region defines a three-dimensional spacefor allowed isocenter positions. For delivery of a radiation treatment,the collision free region defines a three-dimensional space for allowedcouch coordinates. Optionally, a class solution can also include anidentifier, which can be used for example to communicate betweenplanning and delivery. The identifier may include information of aspecific technology solution, for example a version number.

The collision free regions may be visualized by a user to plan for fieldgeometry and isocenter position tradeoffs. In planning, the system maydetermine a field geometry based on a desired isocenter position in apatient. For example, the system may consider multiple field geometryalternatives and select one that is allowed based on the shape of thecorresponding collision free region. As another example, the system mayevaluate collision risks of user-selected fields by checking themagainst collision free regions corresponding to a given isocenterposition. In delivery, the system may evaluate collision risks of thefields of a given treatment plan by checking them against the collisionfree regions of the delivery machine. The system may prevent executionof the treatment plan upon determining that there is collision risks, orthe system may limit the execution of the treatment plan by, forexample, removing the fields that can cause collisions. Alternatively,the system may notify a user that one or more fields may causecollisions.

I. Radiation Treatment System

In general, radiation therapy consists of the use of ionizing radiationto treat living tissue, usually tumors. There are many different typesof ionizing radiation used in radiation therapy, including high energyx-rays, electron beams, and proton beams. The process of administeringthe radiation to a patient can be somewhat generalized regardless of thetype of radiation used. External beam therapy (EBT), also calledexternal radiation therapy, is a method for delivering a beam or severalbeams of high-energy x-rays to a patient's tumor. Beams are generatedoutside the patient (usually by a linear accelerator) and are targetedat the tumor site.

FIGS. 1 and 2 depict a radiation treatment system of the type that maybe used in connection with the present invention. Referring to FIG. 1, aperspective view of radiation treatment system (in this case a linearaccelerator) is shown. Typically, such a system is capable of generatingeither an electron (particle) beam or an x-ray (photon) beam for use inthe radiotherapy treatment of patients on a treatment couch 35. Otherradiation treatment systems are capable of generating heavy ionparticles such as protons. For purposes of the present discussion, onlyx-ray irradiation will be discussed. However, it will be appreciated bythose skilled in the art that the same principles apply to othersystems.

Stand 10 supports a rotatable gantry 20 with a treatment head 30. Nextto stand 10 there is arranged a control unit (not shown) that includescontrol circuitry for controlling the different modes of operation ofthe accelerator. A high voltage source is provided within the stand orin the gantry, to supply voltage to an electron gun (not shown)positioned on an accelerator guide located in the gantry 20. Electronsare emitted from the electron gun into the guide (not shown) where theyare accelerated. A source supplies RF (microwave) power for thegeneration of an electric field within the waveguide. The electronsemitted from the electron gun are accelerated in the waveguide by theelectric field, and exit the waveguide as a high energy electron beam,typically at megavoltage energies. The electron beam then strikes asuitable metal target, emitting high energy x-rays in the forwarddirection.

Referring now to FIG. 2, a somewhat more detailed side view of aradiation treatment system of the type that may be used in connectionwith the present invention is shown. A patient P is shown lying on thetreatment couch 35. X-rays formed as described above are emitted fromthe target in the treatment head 30 in a divergent beam 104. Typically,a patient plane 116, which is perpendicular to the page in FIG. 2, ispositioned about one meter from the x-ray source or target, and the axisof the gantry 20 is located on the plane 116, such that the distancebetween the target and the isocenter 178 remains constant when thegantry 20 is rotated. The isocenter 178 is at the intersection betweenthe patient plane 116 and the central axis of beam 122. A treatmentvolume to be irradiated is located about the isocenter 178.

FIG. 3 shows schematically a photon collimation system 300 with upperjaws 310 (i.e., the Y1 and Y2 jaws; the Y1 jaw is omitted for clarity),lower jaws 320 (i.e., the X1 and X2 jaws), and a multileaf collimator(MLC) 330. The field dimensions in the plane 340 at the isocenter 178are indicated. The upper jaws 310, the lower jaws 320, and the leaves332 of the MLC 330 comprise an x-ray blocking material, and arepositioned in the head 30 to define the width of the x-ray beam at thepatient plane. Typically, the jaws 310 and 320 are moveable and, whenfully open, define a maximum beam of about 40 cm×40 cm at the patientplane 116. The MLC 330 is positioned at the exit of the head 30, tofurther shape the x-ray beam. Since its introduction in 1990 the MLC hasbecome a standard feature of most radiation treatment systems. CurrentMLCs sold by the assignee of the present invention use up to 120individually controllable leaves, typically thin slices of tungsten,that can be moved into or out of the x-ray beam under the control ofsystem software.

FIG. 4 shows an exemplary MLC plane having a plurality of leaves 332,arranged in opposing pairs, and an aperture 415 created by selected leafmovements. Radiation passes through and is shaped by the aperture 415.Thus, the MLC can be used to collimate the x-rays to provide conformaltreatment of tumors from various angles (“3D conformal”) as well asintensity modulated radiotherapy (“IMRT”), whereby different radiationdoses are delivered to different portions of the treatment area. Thetreatment volume, i.e., the irradiated volume proximate to the isocenter178 in the path of the x-ray beam, is defined by the jaws 310 and 320,the leaf sequence of the MLC 330, and the collimator angle, i.e., theangle at which the MLC 330 sits in the head 30. Some external radiationtreatment systems may include multiple layers of MLCs. The multiplelayers of MLCs may be positioned at different planes and at differentcollimator angles.

FIG. 5 shows a block diagram of an external-beam radiation treatmentsystem 500 of FIGS. 1 and 2. The radiation treatment system 500 includesa beam source 510, a beam aperture 520, a gantry 530, and a couch 540.The beam source 510 is configured to generate a beam of therapeuticradiation. This beam of radiation may include x-rays, particles, and thelike. The beam aperture 520 includes an adjustable multi-leavecollimator (MLC) 522 for spatially filtering the radiation beam. Thecouch 540 is configured to support and position a patient. The couch 540may have six degrees of freedom, namely the translational offsets X, Y,and Z, and the rotation, pitch, and yaw.

The gantry 530 that circles about the couch 540 houses the beam source510 and the beam aperture 520. The beam source 510 is optionallyconfigured to generate imaging radiation as well as therapeuticradiation. The radiation treatment system 500 may further include animage acquisition system 550 that comprises one or more imagingdetectors mounted to the gantry 530.

The radiation treatment system 500 further includes a control circuitry560 for controlling the operation of the beam source 510, the beamaperture 520, the gantry 530, the couch 540, and the image acquisitionsystem 550. The control circuitry 560 may include hardware, software,and memory for controlling the operation of these various components ofthe radiation treatment system 500. The control circuitry 560 cancomprise a fixed-purpose hard-wired platform or can comprise a partiallyor wholly-programmable platform. The control circuitry 560 is configuredto carry out one or more steps, actions, and other functions describedherein. In some embodiments, the control circuitry 560 may include amemory for receiving and storing a radiation treatment plan that definesthe control points of one or more treatment fields. The controlcircuitry 560 may then send control signals to the various components ofthe radiation treatment system 500, such as the beam source 510, thebeam aperture 520, the gantry 530, and the couch 540, to execute theradiation treatment plan. In some embodiments, the control circuitry 560may include an optimization engine 562 configured for determining aradiation treatment plan. In some other embodiments, the controlcircuitry 560 may not include an optimization engine. In those cases, aradiation treatment plan may be determined by an optimization engine ina separate computer system, and the radiation treatment plan is thentransmitted to the control circuitry 560 of the radiation treatmentsystem 500 for execution.

II. Radiation Treatment Plans

Radiation treatment is generally implemented in accordance with aradiation treatment plan that typically takes into account the desireddose of radiation that is prescribed to be delivered to the tumor, aswell as the maximum dose of radiation that can be delivered tosurrounding tissue. Various techniques for developing radiationtreatment plans may be used. Preferably, the computer system used todevelop the radiation treatment plan provides an output that can be usedto control the external-beam radiation treatment system, including thecontrol points and the MLC leaf movements.

Typically, such planning starts with volumetric information about thetarget tumor and about any nearby tissue structures. For example, suchinformation may comprise a map of the planning target volume (“PTV”),such as a prostate tumor, which is prescribed by the physician toreceive a certain therapeutic radiation dose with allowable tolerances.Volumetric information about nearby tissues may include for example,maps of the patient's bladder, spinal cord and rectum, each of which maybe deemed an organ at risk (OAR) that can only receive a much lower,maximum prescribed amount of radiation without risk of damage. Thisvolumetric information along with the prescribed dose limits and similarobjectives set by the medical professionals are the basis forcalculating an optimized dose distribution, also referred to as fluencemap, which in turn is the basis for determining a radiation treatmentplan.

A radiation treatment plan, either for radiation therapy orradiosurgery, may include a plurality of treatment fields for deliveringradiation to a patient using an external-beam radiation treatmentsystem. The treatment fields may include stationary treatment fieldswhere the direction of incidence to a treatment target is fixed duringbeam-on, or dynamic treatment fields where the direction of incidence toa treatment target changes during continuous irradiation. A fieldgeometry describes the relation between radiation fields, the patient,and the support devices. In a stationary treatment field, only the MLCleaves and the collimator jaws move, while other treatment axes, such asthe isocenter location, gantry angle, couch angles (including rotation,pitch, and yaw), and couch offsets, are fixed during beam on.

Dynamic treatment fields may include, for example, intensity modulatedarc therapy (IMAT), volumetric modulated arc therapy (VMAT), andconformal arc therapy. For example, a VMAT treatment may involve one ormultiple appropriately optimized intensity-modulated arcs in whichradiation is administered with simultaneous gantry rotation and MLCmotion. In general, a dynamic treatment field may define a trajectory ofsome treatment axes of the external-beam radiation treatment system,such as the isocenter location, gantry angle, couch angles (includingrotation, pitch, and yaw), and couch offsets.

A VMAT arc can be either coplanar or non-coplanar. A coplanar VMAT arcrefers to the case where the couch rotation angle is fixed at zerodegree as the gantry rotates during beam-on. A non-coplanar VMAT arcrefers to the case where the couch rotation angle is fixed at a non-zerodegree angle as the gantry rotates during beam-on, i.e., the couch isnot parallel to the axis of rotation of the gantry. Dynamic treatmentpaths can also include coronal arc, where the gantry is fixed and thecouch rotates during continuous irradiation. Dynamic treatment fieldsenable plans of comparable quality to be delivered in less time.

III. Using Collision Free Regions for Planning Radiation Treatment

When executing a radiation treatment plan using an external-beamradiation treatment system, it is possible that certain fieldgeometries, especially those of dynamic treatment fields, may causemachine-to-machine or machine-to-patient collisions. In such cases,automated execution of the treatment plan may need to be prevented orelse accidents may occur. Therefore, it may be desirable to evaluatecollision possibilities when planning a radiation treatment to ensurethe safety and usability of a radiation treatment plan.

According to some embodiments of the present invention, predeterminedcollision free regions may be used for planning a radiation treatment tomanage collision risks. Collision free regions may be predetermined forone or more class solutions. Each class solution has defined limits forallowed field geometry variations, such as allowed gantry angle rangesand allowed couch parameter ranges. According to an embodiment, acollision free region for planning may be determined for each classsolution based on a machine model and a patient model. A statisticalpatient model, instead of the geometry of an actual patient, may beused. Each collision free region for planning defines athree-dimensional space for allowable isocenter positions for thecorresponding class solution. In some embodiments, the collision freeregions can be visualized by a user on a computer user interface so thatthe user can quickly evaluate possible field geometries and anytrade-offs between field geometries and the isocenter position.

A. Collision Free Regions and Class Solutions

FIG. 6 shows an exemplary user interface that displays some exemplarycollision free regions 610, 620, and 630 for planning a radiationtreatment. In this example, the radiation treatment is for treatingcranial tumors in a patient. A three-dimensional image 602 of the headportion of the patient is superimposed on the collision regions 610,620, and 630. The image can be, for example, a cone-beam computertomography (CBCT) image. A first collision free region 610 (indicated bymagenta outlines) is on the right hand side of the patient's head. Asecond collision free region 620 (indicated by cyan outlines) is on theleft hand side of the patient's head. The common region in the middle,i.e., the intersection of the first collision free region 610 and thesecond collision free region 620, may be defined as a third collisionfree region 630. The three brown balls 652, 654, and 656 are the targetvolumes (e.g., tumors).

FIG. 7 shows the collision free regions 610, 620, and 630, as well asthe image 602 of the patient, as viewed from the patient's feet. A modelpatient support structure 660 (i.e., the U-shaped cyan structure) isalso shown in FIG. 7. Although the collision free regions 610 and 620are shown as boxes, the collision free regions can have more complexgeometric shapes, or can be a set of overlapping or non-overlappingshapes according to some embodiments of the present invention.

Each collision free region 610, 620, or 630 is a three-dimensional spacefor allowed isocenter positions with respect to a corresponding classsolution. That is, if the isocenter is positioned anywhere inside arespective collision free region, any field geometries within the limitsof the corresponding class solution may be delivered without collisionrisk.

A class solution may include one or more predetermined treatment fields.FIG. 8 shows some exemplary treatment fields according to an embodimentof the present invention. In this example, five arcs 870, 872, 874, 876,and 878 are shown. Each of the five arcs is a half-arc. Among them, thearcs 872. 874, and 876 are non-coplanar arcs, and the arcs 870 and 878are coplanar arcs. The two half coplanar arcs 870 and 878 may becombined to form a full arc. In other embodiments, more or fewerpredetermined treatment fields may be used.

Referring to FIGS. 6-8, according to an embodiment, if the isocenter isplaced in the third collision free region 630, i.e., the intersection ofthe first collision free region 610 and the second collision free region620, all five arcs 870, 872, 874, 876, and 878 may be delivered withoutcollision risk. If the isocenter is placed in the first collision freeregion 610 excluding the third collision free region 630, only the arcs870, 872, 874, and 876 can be delivered without collision risk. If theisocenter is placed in the second collision free region 620 excludingthe third collision free region 630, only the arcs 872, 874, 876, and878 can be delivered without collision risk. Thus, the first collisionfree region 610 excluding the third collision free region 630 may beassociated with a first class solution that includes the predeterminedarcs 870, 872, 874, and 876; the second collision free region 620excluding the third collision free region 630 may be associated with asecond class solution that includes the predetermined arcs 872, 874,876, and 878; and the third collision free region 630 may be associatedwith a third class solution that includes all five predetermined arcs870, 872, 874, 876, and 878.

In a radiation treatment, it may be beneficial to place the isocenter inthe middle of a target. On the other hand, it may also be beneficial tohave more fields (arcs) to distribute the radiation dose in a largerregion. When radiation dose is distributed in a larger region from asmany directions as possible, the dose level may drop more quickly movingaway from a target. Therefore, there may be a trade-off between havingthe isocenter close to a target and having as many fields as possible.By enabling a user to visualize on a user interface the collision freeregions in the same coordinate system as that of the image of thepatient, the user may be able to decide more easily the desiredisocenter position considering both the isocenter position relative tothe targets and the field geometries allowed by each class solution.

FIG. 9A shows an exemplary user interface where the collision freeregions 610, 620, and 630 are superimposed on the three-dimensionalimage 602 of the patient as viewed from the patient's feet. Theisocenter is placed within the third collision free region 630 (i.e.,the intersection of the first collision free region 610 and the secondcollision free region 620). Thus, all five predetermined arcs 870, 872,874, 876, and 878 illustrated in FIG. 8 can be delivered withoutcollision risk. FIG. 9A shows the radiation field of one of the arcs872.

FIG. 9B shows a perspective view of the collision free regions 610, 620,and 630 superimposed on the three-dimensional image 602 of the patient.FIG. 9B also shows the radiation field of one of the arcs 872. Each ofFIGS. 9A and 9B also shows a green FIG. 910 on the lower left corner toillustrate patient orientation in the images. The red dot 912 is thepatient's nose, and the red ball 914 is in the patient's left hand.

Because the exact patient position is usually not known at planning(i.e., before the patient has been accurately positioned using imageguided radiation therapy (IGRT) procedures), certain margins may beprovided in determining the shapes of the collision free regions toaccount for necessary corrections in the patient positioning duringdelivery.

B. Patient Registration

When using the collision free regions in planning, a user may need tofirst register an image of a patient with respect to the collision freeregions. According to an embodiment, collision free regions for planningare defined relative to a model fixation device or a patient model thatcontains a fixation device. FIG. 10 shows a model fixation device 1010(shown in cyan color), to which collision free regions are referenced. Afixed point on the model fixation device 1010, for example the point“center” 1012, can be used as a reference point.

FIG. 11A shows an image 1102 of a patient (shown in grey color) asviewed from the right side of the patient. A couch support device 1104is included in the imaging. A model fixation device 1010 (shown in cyancolor) is superimposed on the patient's image 1102. FIG. 11B shows thepatient's image 1102 superimposed on the model fixation device 1010 asviewed from the front of the patient. Before a user starts to plan aradiation treatment using the collision free regions, the user mayregister the patient relative to the collision free regions by aligningthe model fixation device 1010 with the image of the couch supportdevice 1104. For example, the user may use the yellow arrows shown inFIGS. 11A and 11B to move the model fixation device 1010 in threeorthogonal directions, until the model fixation device 1010 is alignedwith the image of the couch support device 1104.

C. Statistical Patient Model

According to an embodiment of the present invention, the shape of thecollision free regions may be determined based on a statistical patientmodel instead of the geometry of an actual patient. A planner (or adelivery person when used in delivery) can estimate whether the geometryof an actual patient fits within the statistical patient model. In someembodiments, the patient model may include a body shape that fits 95% ofa patient population. The information for the 95th percentile of apatient population may be taken from the standard ISO 7250. ISO 7250 isa reputable, common, and readily accessible source of information. Inone embodiment, a statistical patient model has the dimension valuesshown in the table of FIG. 12. All dimensions are expressed in units ofcentimeters unless stated otherwise.

D. Selection of Fields and Isocenter Position

According to an embodiment, a user may be presented with a set ofpredetermined treatment fields and is allowed to select one or moretreatment fields from the set. The set of predetermined treatment fieldsmay be grouped into several class solutions, similar to the exampleillustrated in FIG. 8 as described above. FIG. 13A shows an exemplaryuser interface according to an embodiment of the present invention. Aschematic FIG. 1310 of a patient, as well as five predetermined arcs1370, 1372, 1374, 1376, and 1378, are shown in the user interface. Thearrow for each arc illustrates the direction of execution. A user canselect or deselect an arc by checking the arc on and off. In the exampleillustrated in FIG. 13A, four of the five arcs (1370, 1372, 1374, and1376) are selected as shown by the check signs.

FIG. 13B shows a user interface where the collision free regions 1310and 1320 and the model fixation device 1360, as well as an image 1302 ofa patient, are shown. According to an embodiment, if the isocenter isplaced in the intersection of the first collision free region 1310 andthe second collision free region 1320, all five arcs 1370, 1372, 1374,1376, and 1378 can be delivered without collision risk. If the isocenteris placed in the first collision free region 1310 or the secondcollision free region 1320 excluding the intersection region, only asubset of the five arcs 1370, 1372, 1374, 1276, and 1378 can bedelivered without collision risk. For example, if the isocenter isplaced in the first collision free region 1310 excluding theintersection region, only the arcs 1370, 1372, 1374, 1376 can bedelivered without collision risk. Therefore, all four arcs 1370, 1372,1374, and 1376 selected by the user, as illustrated in FIG. 13A, can bedelivered without collision risk. In FIG. 13B, those four arcs 1370,1372, 1374, and 1376 are shown in the user interface.

In one embodiment, the isocenter position may be manually defined by auser. For example, a user may manually position the isocenter using auser input device (e.g., a mouse) by dragging and dropping the isocentericon. In other embodiments, the system may automatically calculate adesired isocenter position. For example, the system may calculate thedesired isocenter position based on the center of mass of the targets,or a geometrical center point of a smallest box that contains alltargets.

According to one embodiment, if the user placed the isocenter positionin a collision free region where not all user-selected fields can bedelivered without collision risk, the system may allow all theuser-selected fields and automatically move the isocenter into a newcollision free region where all user-selected fields can be deliveredwithout collision risk. For example, if a user has selected all fivearcs 1370, 1372, 1374, 1376, and 1378 shown in FIG. 13A, and has placedthe isocenter position in the first collision region 1310 excluding theintersection region, the system may automatically move the isocenterinto the intersection region. In one embodiment, the system may move theisocenter to as close to the user-selected isocenter position aspossible within the new collision free region.

According to another embodiment, the system may keep the user-selectedisocenter position, and automatically remove those fields that cannot bedelivered without collision risk. For example, if the user has selectedall five arcs 1370, 1372, 1374, 1376, and 1378 shown in FIG. 13A, andhas placed the desired isocenter position in the first collision region1310 excluding the intersection region, the system may keep theuser-selected isocenter position, and automatically remove the arc 1378,e.g., by automatically de-selecting arc 1378.

According to yet another embodiment, the system may allow a user toselect a desired isocenter position, or the system may select a desiredisocenter position (for example based on the center of mass of thetargets). The system may then test the selected isocenter positionagainst multiple class solutions and choose one of them. In oneembodiment, the system may choose a class solution that includes themost allowed fields for the selected isocenter position. For example, ifthe selected isocenter position is in the intersection of the firstcollision free region 1310 and the second collision free region 1320,the system may choose the class solution that includes all five arcs1370, 1372, 1374, 1376, and 1378 illustrated in FIG. 13A. On the otherhand, if the selected isocenter position is in the first collision freeregion 1310 excluding the intersection region, the system may choose theclass solution that includes the arcs 1370, 1372, 1374, and 1376.

It should be noted that a class solution can also include coronal arcs,where the gantry is fixed and the couch coordinate and/or the isocentermoves during continuous irradiation. For such cases, a collision freeregion for the class solution can comprise a three-dimensional space forallowed initial isocenter positions.

E. Method of Determining a Radiation Treatment Plan Using Collision FreeRegions in a First Embodiment

FIG. 14 shows a simplified flowchart illustrating a method 1400 ofdetermining a radiation treatment plan for delivering radiation to apatient using an external-beam radiation treatment system according toan embodiment of the present invention.

At 1402, one or more class solutions are received by a computer system.Each class solution includes field geometry limits for one or moretreatment axes of the external-beam radiation treatment system and acorresponding collision free region. The one or more treatment axes ofthe external-beam radiation treatment system may include, for example,isocenter location, gantry angle, couch angles (rotation, pitch, andyaw), and couch offsets (X, Y, and Z coordinates). The collision freeregion includes a three-dimensional space for allowed initial isocenterpositions determined based on a delivery machine model and a patientmodel.

At 1404, a three-dimensional image of the patient is received by thecomputer system. The three-dimensional image can be, for example, acone-beam computer tomography (CBCT) image. The three-dimensional imageof the patient may include image of one or more target volumes within atreatment area of the patient.

At 1406, the three-dimensional image of the patient is aligned with thecollision free regions of the one or more class solutions. A user mayregister the three-dimensional image of the patient with respect to thecollision free regions by aligning a model fixation device with an imageof a couch support device that is included in the three-dimensionalimage of the patient.

At 1408, a desired initial isocenter position is received. The desiredinitial isocenter position may be input by a user using an input deviceof the user interface. Alternatively, the desired initial isocenterposition may be calculated based on a center of mass of the one or moretarget volumes, or based on a geometrical center point of a smallest boxthat contains the one or more target volumes.

At 1410, it may be determined that the desired initial isocenterposition is within at least one collision free region of the one or moreclass solutions. For example, the system may compare the desired initialisocenter position against the collision free regions corresponding tothe one or more class solutions to determine whether the initialisocenter position falls within the boundary of any collision freeregion.

At 1412, one or more treatment fields within the field geometry limitsof a class solution corresponding to the at least one collision freeregion are identified. Each class solution may include one or morepredetermined treatment fields. In one embodiment, the at least onecollision free region includes one collision free region, andidentifying one or more treatment fields includes identifying thepredetermined treatment fields of the class solution corresponding tothe one collision free region. In another embodiment, the at least onecollision free region may include a plurality of collision free regionscorresponding to a plurality of class solutions, and identifying one ormore treatment fields includes selecting a class solution that includesmost predetermined treatment fields among the plurality of classsolutions.

At 1414, the radiation treatment plan is determined using the one ormore identified treatment fields. The radiation treatment plan mayinclude a control-point sequence and a multileaf collimator (MLC) leafsequence based on the identified one or more treatment fields. Theradiation treatment plan may be transmitted to control circuitry of theexternal-beam radiation treatment system to cause the external-beamradiation treatment system to deliver the radiation to the patientaccording to the control-point sequence and the multileaf collimator(MLC) leaf sequence of the radiation treatment plan.

F. Method of Determining a Radiation Treatment Plan Using Collision FreeRegions in a Second Embodiment

FIG. 15 shows a simplified flowchart illustrating a method 1500 ofdetermining a radiation treatment plan for delivering radiation to apatient using an external-beam radiation treatment system according toanother embodiment of the present invention.

At 1502, one or more class solutions are received by a computer system.Each class solution includes field geometry limits for one or moretreatment axes of the external-beam radiation treatment system and acorresponding collision free region. The collision free region includesa three-dimensional space for allowed initial isocenter positionsdetermined based on a delivery machine model and a patient model.

At 1504, a three-dimensional image of the patient is received by thecomputer system. The three-dimensional image can be, for example, acone-beam computer tomography (CBCT) image. The three-dimensional imageof the patient may include image of one or more target volumes within atreatment area of the patient.

At 1506, the three-dimensional image of the patient is aligned with thecollision free regions of the one or more class solutions. A user mayregister the three-dimensional image of the patient with respect to thecollision free regions by aligning a model fixation device with an imageof a couch support device that is included in the three-dimensionalimage of the patient.

At 1508, a desired initial isocenter position is received. The desiredinitial isocenter position may be input by a user using an input deviceof the user interface. Alternatively, the desired initial isocenterposition may be calculated based on a center of mass of the one or moretarget volumes, or based on a geometrical center point of a smallest boxthat contains the one or more target volumes.

At 1510, a user selection of one or more treatment fields of the one ormore class solutions is received on the user interface. At 1512, it maybe determined that the desired initial isocenter position is within atleast one of the collision free regions. At 1514, a subset of the one ormore user-selected treatment fields may be identified that are withinfield geometry limits of a class solution corresponding to the at leastone of the collision free regions. In some embodiments, the subset ofthe one or more user-selected treatment fields may include all of theone or more user-selected treatment fields.

In some embodiments, identifying the subset of the one or more selectedtreatment fields includes, for each respective treatment field of theone or more user-selected treatment fields, determining whether therespective treatment field is within the field geometry limits of theclass solution corresponding to the at least one of the collision freeregions. Upon determining that the respective treatment field is outsidethe field geometry limits of the class solution corresponding to the atleast one of the collision free regions, the respective treatment fieldmay be excluded from the subset of the one or more user-selectedtreatment fields. Upon determining that the respective treatment fieldis within the field geometry limits of the class solution correspondingto the at least one of the collision free regions, the respectivetreatment field may be included in the subset of the one or moreuser-selected treatment fields.

In some other embodiments, upon determining that at least one of the oneor more user-selected treatment fields is outside the field geometrylimits of the class solution corresponding to the at least one of thecollision free regions, the desired isocenter position is moved to a newisocenter position. The new isocenter position is within anothercollision free region, and all of the one or more user-selectedtreatment fields are within field geometry limits of a class solutioncorresponding to the another collision free region.

At 1516, the radiation treatment plan is determined using the one ormore identified treatment fields. The radiation treatment plan mayinclude a control-point sequence and a multileaf collimator (MLC) leafsequence based on the identified one or more treatment fields. Theradiation treatment plan may be transmitted to control circuitry of theexternal-beam radiation treatment system to cause the external-beamradiation treatment system to deliver the radiation to the patientaccording to the control-point sequence and the multileaf collimator(MLC) leaf sequence of the radiation treatment plan.

IV. Using Collision Free Regions for Delivery of Radiation Treatment

When delivering radiation treatment using a given radiation treatmentplan, whether it was planned using collision free regions as describedabove or planned without using collision free regions, it may bedesirable to verify that the field geometries of the radiation treatmentplan will be collision free in a specific delivery machine.

A. Collision Free Regions in Delivery

According to an embodiment of the present invention, collision freeregions for delivery may be predetermined for one or more classsolutions based on the geometries of the actual delivery machine and apatient model. The collision free regions for delivery may take intoaccount delivery specific margins. Each collision free region fordelivery defines a three-dimensional space for allowable couchcoordinates for a corresponding class solution. That is, if the couchcoordinates reside anywhere inside a respective collision free region,any field geometries within the limits of the corresponding classsolution may be delivered without collision.

FIG. 16 shows an exemplary user interface for using collision freeregions during delivery according to an embodiment of the presentinvention. The blue outline 1630 indicates a boundary of a collisionfree region for allowed couch coordinates. Thus, the couch coordinate“A” should be positioned within the blue outline 1630. The inner redoutline 1610 indicates the boundary of a collision free region used inplanning for allowed isocenter positions. The inner red outline 1612 hassome margins subtracted from the outer red outline 1610 giving somespace for isocenter corrections during delivery, since the precisepatient position is usually not known in planning. Thus, the isocenter“P” should be positioned within the outer red outline 1612 at delivery.The other pair of outer red outline 1620 and inner red outline 1622indicate the boundary of another collision free region used in planningfor allowed isocenter positions.

The model used in delivery may be different from the model used inplanning in several ways. First, the collision free regions in deliverymay be defined relative to absolute machine parameters, whereas thecollision free regions in planning may be defined relative to a modelfixation device as discussed above. Second, in delivery, the collisionrisks are normally evaluated after a patient has been positioned usingimage-guided radiation therapy (IGRT) procedures, whereas the precisepatient position is usually not known in planning. Therefore, largermargins may be provided in the planning model that those provided in thedelivery model according to some embodiments. The aim is to make surethat the couch coordinates generated from the planning isocenter afterthe IGRT position process fall into allowed couch positions in delivery.In the planning stage, some of the information is not available yet. Forexample, IGRT position shift, as well as pitch and roll corrections, maynot be known at planning. The extra margin in planning may ensure thatthe plan is still deliverable even after the IGRT corrections have beenapplied.

B. Evaluating Collision Risk of a Treatment Plan

The fields of a treatment plan can be tested against the collision freeregions in delivery to evaluate collision risks. In delivery, during thepatient positioning using image-guided radiation therapy (IGRT)procedures, a user may have a preview of the couch coordinates and cancheck whether the couch coordinates fall within any collision freeregions, and whether the field geometries and delivery parameters of thetreatment plan are within the limits for allowed field geometryvariations, such as allowed gantry angle ranges and allowed couchparameter ranges, defined by the class solution corresponding to thecollision free region.

In one embodiment, if the delivery parameters are not within allowedlimits, the system may prevent the treatment. In another embodiment, thesystem may notify the user that fields in the treatment plan may causecollision. In a further embodiment, the system may allow the treatmentin a limited way. For example, the system may limit the automation ofthe delivery, such as automatically remove an arc or shorten an arc. Thesystem may also indicate that the treatment axes violate the collisionfree regions and may indicate the amount of the violation. The systemmay also indicate the violation of the collision free regionsgraphically.

C. Collision Free Regions in Planning and in Delivery

The collision free regions for delivery may be independent from thecollision free regions for planning. But in some embodiments, classsolutions in delivery may be linked to class solutions in planning. Thatis, each class solution in planning may have a corresponding model indelivery. In one embodiment, an identifier can be used for each classsolution to communicate between planning and delivery. The identifiermay also identify a specific technology solution, such as a versionnumber. A plan that is collision free according to the model in planningis likely also collision free in the corresponding model in delivery.

By having independent collision free regions in planning and delivery,it may be possible to change the machine to a dosimetrically equivalentmachine with different geometric parameters. Sometimes machines arecalibrated so that they are dosimetrically equivalent, although thepatient support devices may vary. For example, the couch dimensions maybe different. Therefore the collision free regions may be different. Ifa treatment plan is to be delivered with a delivery machine that isdifferent from the model machine used in planning, the delivery machinecan evaluate collision risks of the field geometries of the treatmentplan against the collision free regions of its own collision model.

In some embodiments, a delivery machine can evaluate collision risks fortreatment plans that are not planned with a planning system consideringcollision free regions. For example, the delivery system may identifythat the field geometries of a plan are within a specific classsolution. Upon determining that the plan is within the limits of a classsolution, certain additional functionality may be enabled. For example,the user may be notified that the plan is within the limits of a classsolution. Full automation of the execution of the treatment plan may beenabled upon determining that a plan is within the limits of a classsolution. More automation may help to reduce delivery time, which may beespecially desirable in radiosurgery applications.

Because the evaluations of collision risks in planning and delivery areindependent, changing a machine configuration, such as couchcalibration, may not require re-planning or re-evaluation of collisionrisks. For example, a couch recalibration may affect the absolute couchcoordinates and therefore may affect the collision free regions of thetarget machine. However, a plan that is generated for the previous couchcalibration and has been determined to be collision-free is likely to becollision-free for the new couch calibration as well, since therelationship between the collision free regions and the couchcoordinates before and after the recalibration should be the same.

D. Method of Delivering Radiation to a Patient Using Collision FreeRegions

FIG. 17 shows a simplified flowchart illustrating a method 1700 ofdelivering radiation to a patient using an external-beam radiationtreatment system according to an embodiment of the present invention.

At 1702, one or more class solutions are received by a computer systemcommunicably coupled with the external-beam radiation treatment system.Each class solution includes field geometry limits for one or moretreatment axes of the external-beam radiation treatment system and acorresponding collision free region. the collision free region includesa three-dimensional space for allowed couch coordinates determined basedon a model of a delivery machine and a patient model.

At 1704, a radiation treatment plan is received by the computer system.The radiation treatment plan may include one or more treatment fields.The radiation treatment plan may be determined using collision freeregions or without using collision free regions, as discussed above.

At 1706, a three-dimensional image of the patient is acquired by theexternal-beam radiation treatment system. The three-dimensional imagecan be, for example, a cone-beam computer tomography (CBCT) image.

At 1708, the patient is positioned by external-beam radiation treatmentsystem based on the three-dimensional image of the patient to obtain anactual couch coordinate. For example, the patient may be positionedusing image-guided radiation therapy (IGRT) procedures.

At 1710, it may be determined whether the actual couch coordinate iswithin at least one collision free region. For example, the system maycompare the actual couch coordinate against the collision regionscorresponding to the one or more class solutions to determine whetherthe actual couch coordinate falls within the boundary of any of thecollision regions.

At 1712, execution of the radiation treatment plan may be prevented orperformed based on whether the actual couch coordinate is within atleast one collision free region.

In some embodiments, upon determining that the actual couch coordinateis not within any collision free region, execution of the radiationtreatment plan is prevented. Upon determining that the actual couchcoordinate is within at least one collision free region, it may bedetermined whether the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of a class solutioncorresponding to the at least one collision free region. Upondetermining that at least one of the one or more treatment fields of theradiation treatment plan is outside the field geometry limits of theclass solution corresponding to the at least one collision free region,execution of the radiation treatment plan is prevented. A user may benotified that at least one of the one or more treatment fields of theradiation treatment plan is outside the field geometry limits of theclass solution corresponding to the at least one collision free region.

In some other embodiments, upon determining that the actual couchcoordinate is within at least one collision free region, it may bedetermined whether the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of a class solutioncorresponding to the at least one collision free region. Upondetermining that the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of the classsolution corresponding to the at least one collision free region,automatic execution of the radiation treatment plan may be enabled.

In some further embodiments, upon determining that the actual couchcoordinate is within at least one collision free region, it may bedetermined whether the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of a class solutioncorresponding to the at least one collision free region. Upondetermining that at least one treatment field of the one or moretreatment fields of the radiation treatment plan is outside the fieldgeometry limits of the class solution corresponding to the at least onecollision free region, the at least one treatment field is removed fromthe treatment plan, and the radiation treatment plan is executed.

As described above, embodiments of the present invention provide toolsfor managing collision risks for planning and delivery of radiationtreatment. Such tools may increase the robustness of the planning anddelivery process especially for non-coplanar treatment. Non-coplanartreatment fields have been increasingly used in cranial andextra-cranial radiosurgery. Higher doses and smaller number of fractionsare typically used in radiosurgery. Therefore the dose fall-off fromtarget may need to be sharper in order to avoid excessive dose tocritical structures and non-tumorous tissue. The sharper fall-off isnormally achieved by more complex field geometries and use of multiplearcs. The time to deliver these more complex treatments is usuallylonger and collision risks may become more difficult to estimate.

V. Computer System

Any of the computer systems mentioned herein may utilize any suitablenumber of subsystems. Examples of such subsystems are shown in FIG. 18in computer system 1800. In some embodiments, a computer system includesa single computer apparatus, where the subsystems can be the componentsof the computer apparatus. In other embodiments, a computer system caninclude multiple computer apparatuses, each being a subsystem, withinternal components.

The subsystems shown in FIG. 18 are interconnected via a system bus1875. Additional subsystems such as a printer 1874, keyboard 1878,storage device(s) 1879, monitor 1876, which is coupled to displayadapter 1882, and others are shown. Peripherals and input/output (I/O)devices, which couple to I/O controller 1871, can be connected to thecomputer system by any number of means known in the art, such as serialport 1877. For example, serial port 1877 or external interface 1881(e.g. Ethernet, Wi-Fi, etc.) can be used to connect computer system 1800to a wide area network such as the Internet, a mouse input device, or ascanner. The interconnection via system bus 1875 allows the centralprocessor 1873 to communicate with each subsystem and to control theexecution of instructions from system memory 1872 or the storagedevice(s) 1879 (e.g., a fixed disk, such as a hard drive or opticaldisk), as well as the exchange of information between subsystems. Thesystem memory 1872 and/or the storage device(s) 1879 may embody acomputer readable medium. Any of the data mentioned herein can be outputfrom one component to another component and can be output to the user.

A computer system can include a plurality of the same components orsubsystems, e.g., connected together by external interface 1881 or by aninternal interface. In some embodiments, computer systems, subsystem, orapparatuses can communicate over a network. In such instances, onecomputer can be considered a client and another computer a server, whereeach can be part of a same computer system. A client and a server caneach include multiple systems, subsystems, or components.

It should be understood that any of the embodiments of the presentinvention can be implemented in the form of control logic using hardware(e.g. an application specific integrated circuit or field programmablegate array) and/or using computer software with a generally programmableprocessor in a modular or integrated manner. As used herein, a processorincludes a multi-core processor on a same integrated chip, or multipleprocessing units on a single circuit board or networked. Based on thedisclosure and teachings provided herein, a person of ordinary skill inthe art will know and appreciate other ways and/or methods to implementembodiments of the present invention using hardware and a combination ofhardware and software.

Any of the software components or functions described in thisapplication may be implemented as software code to be executed by aprocessor using any suitable computer language such as, for example,Java, C++ or Perl using, for example, conventional or object-orientedtechniques. The software code may be stored as a series of instructionsor commands on a computer readable medium for storage and/ortransmission, suitable media include random access memory (RAM), a readonly memory (ROM), a magnetic medium such as a hard-drive or a floppydisk, or an optical medium such as a compact disk (CD) or DVD (digitalversatile disk), flash memory, and the like. The computer readablemedium may be any combination of such storage or transmission devices.

Such programs may also be encoded and transmitted using carrier signalsadapted for transmission via wired, optical, and/or wireless networksconforming to a variety of protocols, including the Internet. As such, acomputer readable medium according to an embodiment of the presentinvention may be created using a data signal encoded with such programs.Computer readable media encoded with the program code may be packagedwith a compatible device or provided separately from other devices(e.g., via Internet download). Any such computer readable medium mayreside on or within a single computer product (e.g. a hard drive, a CD,or an entire computer system), and may be present on or within differentcomputer products within a system or network. A computer system mayinclude a monitor, printer, or other suitable display for providing anyof the results mentioned herein to a user.

Any of the methods described herein may be totally or partiallyperformed with a computer system including one or more processors, whichcan be configured to perform the steps. Thus, embodiments can bedirected to computer systems configured to perform the steps of any ofthe methods described herein, potentially with different componentsperforming a respective steps or a respective group of steps. Althoughpresented as numbered steps, steps of methods herein can be performed ata same time or in a different order. Additionally, portions of thesesteps may be used with portions of other steps from other methods. Also,all or portions of a step may be optional. Additionally, any of thesteps of any of the methods can be performed with modules, circuits, orother means for performing these steps.

The specific details of particular embodiments may be combined in anysuitable manner without departing from the spirit and scope ofembodiments of the invention. However, other embodiments of theinvention may be directed to specific embodiments relating to eachindividual aspect, or specific combinations of these individual aspects.

The above description of exemplary embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdescribed, and many modifications and variations are possible in lightof the teaching above. The embodiments were chosen and described inorder to best explain the principles of the invention and its practicalapplications to thereby enable others skilled in the art to best utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated.

A recitation of “a”, “an” or “the” is intended to mean “one or more”unless specifically indicated to the contrary.

All patents, patent applications, publications, and descriptionsmentioned here are incorporated by reference in their entirety for allpurposes. None is admitted to be prior art.

What is claimed is:
 1. A method of determining a radiation treatmentplan for delivering radiation to a patient using an external-beamradiation treatment system, the method comprising: receiving, by acomputer system, one or more class solutions, wherein each classsolution includes field geometry limits for one or more treatment axesof the external-beam radiation treatment system and a correspondingcollision free region, and wherein the collision free region comprises athree-dimensional space for allowed initial isocenter positionsdetermined based on a delivery machine model and a patient model;receiving, by the computer system, a three-dimensional image of thepatient; aligning the three-dimensional image of the patient with thecollision free regions of the one or more class solutions; receiving,via a user interface, a desired initial isocenter position; determining,by the computer system, that the desired initial isocenter position iswithin at least one collision free region of the one or more classsolutions; identifying, by the computer system, one or more treatmentfields within the field geometry limits of a class solutioncorresponding to the at least one collision free region; anddetermining, by the computer system, the radiation treatment plan usingthe one or more identified treatment fields.
 2. The method of claim 1,further comprising displaying on the user interface of the computersystem the collision free regions of the one or more class solutions andthe three-dimensional image of the patient.
 3. The method of claim 1,wherein the three-dimensional image of the patient includes image of oneor more target volumes within a treatment area of the patient.
 4. Themethod of claim 3, wherein the desired isocenter position is input by auser using an input device of the user interface.
 5. The method of claim3, wherein the desired isocenter position is calculated based on acenter of mass of the one or more target volumes or based on ageometrical center point of a smallest box that contains the one or moretarget volumes.
 6. The method of claim 1, wherein: each class solutionincludes one or more predetermined treatment fields; determining thatthe desired isocenter position is within at least one collision freeregion comprises determining that the desired isocenter position iswithin a plurality of collision free regions corresponding to aplurality of class solutions; and identifying one or more treatmentfields comprises selecting a class solution that includes mostpredetermined treatment fields among the plurality of class solutions,wherein the one or more identified treatment fields include thepredetermined treatment fields of the selected class solution.
 7. Themethod of claim 1, wherein: the collision free regions are definedrelative to a model fixation device; the three-dimensional image of thepatient is acquired as the patient is fixed to a fixation device, thethree-dimensional image including image of the fixation device; and themodel fixation device is aligned with the image of the fixation devicein the display of the collision free regions and the three-dimensionalimage of the patient.
 8. The method of claim 1, wherein the patientmodel comprises a statistical patient model.
 9. The method of claim 1,wherein the radiation treatment plan includes a control-point sequenceand a multileaf collimator (MLC) leaf sequence based on the identifiedone or more treatment fields, and the method further comprising:transmitting the radiation treatment plan to control circuitry of theexternal-beam radiation treatment system to cause the external-beamradiation treatment system to deliver the radiation to the patientaccording to the control-point sequence and the multileaf collimator(MLC) leaf sequence of the radiation treatment plan.
 10. A method ofdetermining a radiation treatment plan for delivering radiation to apatient using an external-beam radiation treatment system, the methodcomprising: receiving, by a computer system, one or more classsolutions, wherein each class solution includes field geometry limitsfor one or more treatment axes of the external-beam radiation treatmentsystem and a corresponding collision free region, and wherein thecollision free region comprises a three-dimensional space for allowedinitial isocenter positions determined based on a model of a deliverymachine and a patient model; receiving, by the computer system, athree-dimensional image of the patient; aligning the three-dimensionalimage of the patient with the collision free regions of the one or moreclass solutions; receiving, via a user interface, a desired initialisocenter position; receiving, on the user interface, a user selectionof one or more treatment fields of the one or more class solutions;determining that the desired initial isocenter position is within atleast one of the collision free regions; identifying a subset of the oneor more user-selected treatment fields that are within field geometrylimits of a class solution corresponding to the at least one of thecollision free regions; and determining the radiation treatment planusing the subset of the one or more user-selected treatment fields. 11.The method of claim 10, further comprising displaying on the userinterface of the computer system the collision free regions of the oneor more class solutions and the three-dimensional image of the patient.12. The method of claim 10, wherein the subset of the one or moreuser-selected treatment fields includes all of the one or moreuser-selected treatment fields.
 13. The method of claim 10, whereinidentifying the subset of the one or more selected treatment fieldscomprises: for each respective treatment field of the one or moreuser-selected treatment fields, determining whether the respectivetreatment field is within the field geometry limits of the classsolution corresponding to the at least one of the collision freeregions; upon determining that the respective treatment field is outsidethe field geometry limits of the class solution corresponding to the atleast one of the collision free regions, excluding the respectivetreatment field from the subset of the one or more user-selectedtreatment fields; and upon determining that the respective treatmentfield is within the field geometry limits of the class solutioncorresponding to the at least one of the collision free regions,including the respective treatment field in the subset of the one ormore user-selected treatment fields.
 14. The method of claim 10, whereinthe method further comprising: upon determining that at least one of theone or more user-selected treatment fields is outside the field geometrylimits of the class solution corresponding to the at least one of thecollision free regions, moving the desired isocenter position to a newisocenter position, wherein the new isocenter position is within anothercollision free region, and wherein all of the one or more user-selectedtreatment fields are within field geometry limits of a class solutioncorresponding to the another collision free region.
 15. The method ofclaim 10, wherein the desired isocenter position is input by a userusing an input device of the user interface.
 16. The method of claim 10,wherein the desired isocenter position is calculated based on a centerof mass of the one or more target volumes or based on a geometricalcenter point of a smallest box that contains the one or more targetvolumes.
 17. A method of delivering radiation to a patient using anexternal-beam radiation treatment system, the method comprising:receiving, by a computer system communicably coupled with theexternal-beam radiation treatment system, one or more class solutions,wherein each class solution includes field geometry limits for one ormore treatment axes of the external-beam radiation treatment system anda corresponding collision free region, and wherein the collision freeregion comprises a three-dimensional space for allowed couch coordinatesdetermined based on a model of a delivery machine and a patient model;receiving, by the computer system, a radiation treatment plan includingone or more treatment fields; acquiring, by the external-beam radiationtreatment system, a three-dimensional image of the patient; positioning,by external-beam radiation treatment system, the patient based on thethree-dimensional image of the patient to obtain an actual couchcoordinate; determining whether the actual couch coordinate is within atleast one collision free region; and preventing execution of theradiation treatment plan or executing the radiation treatment plan basedon whether the actual couch coordinate is within at least one collisionfree region.
 18. The method of claim 17, wherein preventing execution ofthe radiation treatment plan or executing the radiation treatment plancomprises: upon determining that the actual couch coordinate is notwithin any collision free region, preventing execution of the radiationtreatment plan.
 19. The method of claim 17, wherein preventing executionof the radiation treatment plan or executing the radiation treatmentplan comprises: upon determining that the actual couch coordinate is notwithin any collision free region, preventing automation of the executionof the radiation treatment plan.
 20. The method of claim 17, whereinpreventing execution of the radiation treatment plan or executing theradiation treatment plan comprises: upon determining that the actualcouch coordinate is within at least one collision free region,determining whether the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of a class solutioncorresponding to the at least one collision free region; upondetermining that at least one of the one or more treatment fields of theradiation treatment plan is outside the field geometry limits of theclass solution corresponding to the at least one collision free region,preventing execution of the radiation treatment plan.
 21. The method ofclaim 20, further comprising: notifying a user that at least one of theone or more treatment fields of the radiation treatment plan is outsidethe field geometry limits of the class solution corresponding to the atleast one collision free region.
 22. The method of claim 17, whereinpreventing execution of the radiation treatment plan or executing theradiation treatment plan comprises: upon determining that the actualcouch coordinate is within at least one collision free region,determining whether the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of a class solutioncorresponding to the at least one collision free region; upondetermining that the one or more treatment fields of the radiationtreatment plan are within the field geometry limits of the classsolution corresponding to the at least one collision free region,enabling automatic execution of the radiation treatment plan.
 23. Themethod of claim 17, wherein preventing execution of the radiationtreatment plan or executing the radiation treatment plan comprises: upondetermining that the actual couch coordinate is within at least onecollision free region, determining whether the one or more treatmentfields of the radiation treatment plan are within the field geometrylimits of a class solution corresponding to the at least one collisionfree region; upon determining that at least one treatment field of theone or more treatment fields of the radiation treatment plan is outsidethe field geometry limits of the class solution corresponding to the atleast one collision free region, removing the at least one treatmentfield from the treatment plan; and executing the radiation treatmentplan.